In a digitally controlled printing system, such as an inkjet printing system, a print media is directed through a series of components. The print media can be a cut sheet or a continuous web. A web or cut sheet transport system physically moves the print media through the printing system. As the print media moves through the printing system, liquid, for example, ink, is applied to the print media by one or more printheads through a process commonly referred to as jetting of the liquid. The jetting of liquid onto the print media introduces significant moisture content to the print media, particularly when the system is used to print multiple colors on a print media. Due to its moisture content, the print media expands and contracts in a non-isotropic manner often with significant hysteresis. The continual change of dimensional characteristics of the print media often adversely affects image quality. Although drying is used to remove moisture from the print media, drying too frequently, for example, after printing each color, also causes changes in the dimensional characteristics of the print media that often adversely affects image quality.
FIG. 1 is a schematic of a portion of the print media as the print media passes over two conventional rollers that support the print media under each row of printheads. During an inkjet printing process, the print media can expand as the print media absorbs the water-based inks applied to it. When the direction of expansion is in a direction that is perpendicular to the direction of media travel 100, it is often referred to as expansion in the crosstrack direction 102. Typically, the wrap of the print media around a roller of an inkjet printing system produces sufficient friction between the print media and the roller that the print media is not free to slide in the crosstrack direction even though the print media is expanding in that direction. This can result in localized buckling of the print media away from the roller to create lengthwise ripples, also called flutes or wrinkles, in the print media. Flutes or ridges 104, 106 can be produced in the print media due to expansion of the print media in the crosstrack direction 102 because the print media cannot slip on the rollers 108, 110. Flutes can become permanent creases in the paper as the print media passes over a roller if the flutes have sufficient height as the print media approaches the roller and the wrap angle of the print media is high.
A number of solutions have been proposed to decrease the propensity of the print media to crease, such as ribbed rollers described in U.S. Pat. No. 8,303,106 to Kasiske, Jr. et al., issued Nov. 6, 2012, entitled “Printing system including web media moving apparatus,” and profiled rollers described in co-pending U.S. patent application Ser. No. 14/106,911 to Piatt et al., filed Dec. 16, 2013, entitled “Transport using peaked web guide and roller,” both included in their entirety herein by reference. These rollers act to spread the media during the wrap. These methods have met with measured success but there is an ongoing need to provide digital printing systems and processes with the ability to effectively handle print media expansion associated with the absorption of water by the print media.